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Radiation Protection Flashcards

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1
Q

Background radiation dose to a member of public??

A

2.5mSv

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2
Q

What is Air Kerma?

A

Total Kinetic energy released per unit mass by an ionising radiation

Units Gy

Measurement in air used as air has a similar atomic number to soft tissue (7) and effect on radiation on changes in temp are so small that they can be ignored.

At lower dose: AIR KERMA = ABSORBED DOSE

At higher doses: AIR KERMA > ABSORBED DOSE

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3
Q

Absorbed dose?

A

Amount of deposited energy in a substance

Units of Gy

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4
Q

Relationship between:

Absorbed dose

Equivilent dose

Effective dose

A

Absorbed dose in Gy

multiply by Radiation weighting factor

Equivilent dose in Sv

multiply by tissue weighting factor (had no units)

Effective dose in Sv
(absorbed dose weighted for ratiosensitvity of tissue)

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5
Q

What is Radiation weighting factor?

A

Takes into account effects of different types of radiation

Alpha particles highest: 20

Protons: 2

X-ray, beta, gamma, positrons: 1

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6
Q

Does effective dose relate to stochastic or deterministic effect?

A

Risk of stochastic effects in linked to the EFFECTIVE DOSE

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7
Q

What are the tissue weighting factors?

A

A value given to the different organ sensitivies to radiation

Bone, colon, lung, breast: 0.12

Gonads: 0.08

Skin and brain: 0.01

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8
Q

When is the highest risk to the fetus?

A

All or nothing effect during early fetal stage (0 - 2 weeks)

First trimester is very sensitive: high incidence of congenital malformations

Childhood cancer biggest risk in FIRST TRIMESTER

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9
Q

What is threshold dose for CNS malformations to fetus?

A

100 - 200mGy

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10
Q

When to suspend breastfeeding?

A

Completly if: had course of I131

3 weeks if:

  • I131, I125
  • Gallium
  • Sodium
  • Thallium

12 hours after:

  • Iodine 131 hippurate
  • All Technetium 99m compounts (except Tc red cells which is 4 hours)

4 hours:

  • Technetium 99m red cells
  • DTPA
  • Phosphonates
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11
Q

Effective Dose limits for employee >18years

(Effective Dose governs STOCHASTIC effect risk)

A

20mSv per year

or

100mSv in any consecutive 5 years (with a max of 50mSv per any single year)

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12
Q

Effective dose limits for trainee <18 years

A

6mSv

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13
Q

Effective dose limit for <16 year (trainee or anyone)

A

1mSv per year

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14
Q

Dose to abdomen for person of reproductive capacity (STAFF)

A

13mSv in any consecutive 3 months

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15
Q

What is DAP?

A

DAP = entrance skin dose x cross sectional area of x-ray beam

  • A measure of patient exposure
  • Not affected by distance

Units Gy/cm2

The DAP meter must intercept the ENTIRE area of the x-ray beam

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16
Q

Equivilent dose limits?

Deterministic

A

Lens: 20mSv over 18 years

15mSv under 18 years and indirectly from another person

Extremeties and Skin: 500mSv over 18 years

150mSv for under 18 years

50mSv for thosse exposed indirectly after exposure of another person

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17
Q

What is controlled area?

4 points

A

Where person working their may be subject to:

  1. Effective dose >6mSv
  2. Lens dose 15mSv
  3. Equivilent dose of 3/10 of any relevant dose limit
  4. External dose rates 7.5microSv/hour averaged over the day
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18
Q

What is supervised area?

A

If anyone in the area is likely to receive a dose of 1mSv/year or 1/10th or any dose limit

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19
Q

When to notify HSE?

A
  • Doses exceed staff dose limits
  • Exposures much greater than intended
  • Loss or theft or source
  • Release of spillage leading to significant contamination
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20
Q

What is yearly background radiation dose?

A

2.7mSv approx

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21
Q

Radiation dose - flights etc

A
  • Transatlantic flight: 0.08mSv
  • Nucleur power station worker: 0.18mSv
  • Annual average radon dose: 1.3mSv (out of total 2.7mSv average) - over 50% of dose
  • Average annual radon dose in Cornwall: 6.9mSv

Radon gas emits alpha particles

Medical contribution = 14% to yearly dose

  • CT contributes 47% of medical dose and is only 4% of exams

Nucleur Fallout (from testing of Nucleur weapons years ago)

  • dose is so minimum, just 0.2%
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22
Q

What causes direct damage to tissues?

A

Rupture of Covalent bonds

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23
Q

What causes indirect damage to tissues?

A

Production of free radicals

Free radicals cause chemical changes in tissues

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24
Q

Are absorbed doses higher or lower than effective dose?

A

Absorbed doses tend to be higher

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25
Q

What is the average radiation dose per hour of flying?

A

4µSv/hour

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26
Q

What do tissue weighting factors give an indication of?

A

An estimate of the MORTALITY from cancers per mSv to that organ or tissue

Do not account for likelihood of getting cancer

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27
Q

Does Skin and Bone surface have same tissue weighting factor?

A

Yes

0.01

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28
Q

Deterministic dose effects

A

Lowest is fetal abnormality is 0.1 - 0.5Gy

Most things is 2 - 5Gy

Cataracts is 5Gy

Fatal whole body dose is 5Gy

Deterministic effect gets more severe as dose increases

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29
Q

What is equivilent dose limit for the abdomen of a female employee of reproductive age?

A

13mSv in 3 months

30
Q

Who has overall responsibility for radiation protection?

A

Employer

31
Q

What is justification?

A

Justification to carry out or decline an examination if:

  • benefit of doing exam outweighs risk (carry out exam)
  • benefit of doing exam does not outweigh risk (decline to do exam)
32
Q

Governing body of IRR?

A

HSE (Health and safety excecutive)

33
Q

Gornerning body of IRMER for reporting overexposures to patients?

A

CQE (Care quality commission)

34
Q

Barium doses

A

Barium meal - 3mSv

Barium enema - 7mSv

35
Q

Does absorbed dose depend on organ mass?

A

NO

36
Q

Time of greatest risk of foetal abnormalities?

A

First trimerster

3 - 8 weeks

37
Q

Mental retardation?

A

First and second trimester

8 - 15th week

38
Q

Childhood cancer risk?

A

Maximal in first trimester

39
Q

Risk of fatal cancer from exposure?

A

1 in 20,000 per mSv

Or 5% per sievert

40
Q

Risk of childhood cancer from exposure in utero?

A

1 in 33,000 per mGy

3% per gray

41
Q

What does radon produce?

A

Alpha particles

42
Q

What can DAP ionisation chamber be used for?

A
  • x-ray
  • fluoro

NOT CT

43
Q

TLDs

A

Have:

  • linear response over wide dose range
  • generally used with filters
  • can be reused. can only be read out once
  • can detect shallow and deep doses
  • Have similar sensitivity to film dose badges
  • can measure finger and eye doses
  • Precision of 15% for low doses
  • Precision of 3% for high doses

Need heated to 300 degrees for read out

Need to be annealed after read out

TLD holder helps differentiate between skin and deeper doses

Disadvantages:

  • cannot measure dose rate
  • cannot differentiate between radiation types
  • affected by heat
44
Q

Film Badges

A

Advantages:

  • can identify type of exposure
  • Highly energy depdendent due to the different atomic numbers of Silver and Bromide
  • sensitivity is 0.1mSv
  • use double sided film emulsion (without a screen)
  • similar sensitivity to TLDs
  • provide a permanent record
  • can detect beta radiation and radioactive splash

No intensifier on a film badge

Disadvantages:

  • prone to fogging
  • must be developed and read out
  • require calibration
45
Q

OSL Badges

Optically stimulated luminescence

A

Use aluminium oxide

Intensity of luminescence is proportional to the absorbed dose

Can read dose as low as 0.01mSv

46
Q

Electronic dosimeters

A
  • Accurate to 1µSv
  • Require a filter
  • 100 times more sensitive than TLDs
  • Provide a direct reading
  • can be used to detect radioactive contamination

ARE HIGHLY ENERGY DEPENDENT

  • Geiger muller counters are counted as electronic dosimeters too
47
Q

Can secondary electrons cause ionization?

A

Yes

48
Q

Are writing protocols for doses and having medical physics expert part of IRMER or IRR?

A

Part of IRMER

49
Q

Radiation protection supervisor duties?

A
  • Investigation of excessive doses
  • ensuring staff follow local rules
  • ensuring QA processes in place
  • risk assessment for pregnant staff
50
Q

Can DAP be converted into effective dose?

A

Yes

  • Can be converted into EFFECTIVE DOSE using conversion factor
  • Conversion factors depend on the region of the body
51
Q

DRLs

Are they set locally?

A
  • Are set for standard sized patients (not taken into account for overweight folk)
  • Yes they are set locally by employer but they must be close to the nationally set DRLs

DRLs are set using ESD, screening times and DAP as references

52
Q

Wall protection requirements?

A

Lead - 2mm

Concrete - 1.5cm

Barium plaster - 2cm

Brick - 2.4cm

(equals 2mm of lead)

53
Q

Pregnant worker

A

Should inform EMPLOYER

Should not need to alter her working practice

54
Q

Pointers

A
  • Leakage of radiation should be less than 1mGy per hour at distance of 1m
  • Operator should stand 2m from x ray tube
  • Filtration in dentistry is 1.5mm aluminium
  • Lead apron 45 x 40cm long
55
Q

Does risk of stochastic effects increase LINEARLY or exponentially with dose?

A

Increases Linearly

Known as the Linear no threshold theory

Increased risk with lower age (kids more likely to get a cancer than an adult)

For stochastic effects:

  • Risk of leukaemia is usually peaking at around 7 years
  • Risk of solid organ tumour is around 40 years
56
Q

Who are overexposures due to equipment fault reported to?

A

Has to reported under IRR if it is due to equipment

Reported to HSE

57
Q

IRR

A
  • Employer must state their intention to HSE about using ionising equipment for FIRST time (not for equipement change)
  • Employers responsibilty to perform a risk assessment before installing new equipment (not manufacturers responsibility)
58
Q

Yearly effective dose limit for:

Adults/Under 18/Carer comforter

A

Adult >18: 20mSv

Under 18: 6mSv

Member of public or under 16: 1mSv

Carer of comforter: 5mSv in any period over 5 years

59
Q

Who governs testing of equipment?

A

IRMER and IRR

60
Q

What is a dose constraint?

A

It is the maximum dose than can be exceeded

61
Q

Dose to adults per year. Can it exceed 20mSv/year?

A

Yes it can as long as it doesnt exceed:

50mSv in a single year

100mSv over 5 years

62
Q

What can DRLs be expressed as?

A
  • Screening time
  • mA
  • kV
  • DAP
63
Q

How much radiation does lead apron transmit? 0.35mm

A

0.35mm transmits 3%

0.25mm transmits 5%

64
Q

What are the remainder organs in tissue weighting factors?

A
  • Kidneys
  • Adrenal
  • Gallbladder
  • Heart
  • Lymph nodes
  • Muscles
  • Pancreas
  • Uterus
  • Prostate
  • Small bowel
  • Thymus

All 0.01 each

65
Q

Changes new in IRR17

A
66
Q

Lead Aprons

A
67
Q

Radiation Doses for different exams

A
68
Q

Radiation protection advisor and medical physics expert

IRMER or IRR

A

Medical physics expert - IRMER

RPA - IRR

69
Q

RPS and RPA

A
70
Q

Is equivilent dose used to set occupational dose organ limits?

A

Yes

Physics (10 decks)

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